Acid treatment of coking coals



Patented Dec. 7, 1943 ACID TREATMENT OF coma cons Clayton S. Wolf, New Haven, Conn.,

assi nor, by

mesne assignments, to American Company, New York, N. Maine Y a corporation or No Drawing. Application Filly-2, 1940. Serial No. 343.553

9 Claims.

The present invention relates to the treatment of coking coals and more particularly it relates to a method for altering the coking characteristics of bituminous coals by treatment with chemical reagents.

In the carbonization of bituminous coals difficulties are often encountered because of intense swelling and caking of the coal when passing through the plastic temperature range. Therefore, in coking bituminous coals it is usually necessary to determine the maximum rate of temperature, rise, that is, degrees per minute rise, to which the coal can be subjected while passing through the'plastic temperature range without undue swelling and eaking. This maximum rate of temperature rise varies considerably with difierent coals. For example, the Pittsburgh seam coals are high volatile-containing, highly-swelh ing and caking coals and can only stand a tem perature or about C. per minute through the plastictemperature range. The Beckley seam coals on the other hand, are somewhat less highly swelling coking coals and can be carbonized at a temperature rise oi. about 2 (I. per minute through the plastic range. When coking bituminous coals are formed into briquettes and then the briquettes subjected to carbonization, additional factors must be considered because some binders have swelling properties and may have a softening or fluxing action on the coal itself, or they may lack sumcient binding strength to permit the briquettes in the lower portion of keeping the coal elevated to this temperature for' a period of time varying from 24 to 125 hours, depending upon the particular coal being treated. From a practical standpoint such a process has the serious disadvantage that it requires a long period of time to produce the desired results. An improved oxidation process is described in the copending application of William J. Kruppa, serial No. 343,518, filed July 2, 194.0, in which very finely ground coal is subjected to pressure in the presence of an oxidizing gas in a, closed vessel while at the same time being maintained at an elevated temperature. In this process many coals are suficiently oxidized in a period of only about four hours. Another method of reducing the time requirement is described in my copending application, Serial No. 343,511, filed July 2, 1940, in which the finely ground coal is heated to a temperature of about 150 C. and then subjected to alternate vacuum and atmospheric treatments in a closed vessel. In this process the coals are sufliciently oxidized in lessthan the coking ovens to bear a superimposed head load of the briquettes above. It is therefore desirable that methods of altering the coking characteristics of bituminous coals be developed whichwill permit a higher rate of temperature, rise while passing through the plastic temperature range and also which will permit the use of a 4 wvider range of binding substances in the'manufacture oi briquettes.

It is well known that the tendency of a given coking bituminous coal to swell and cake when subjected to carbonization can be reduced it this two hours. While the oxidizing processes described in the copending applications above have overcome the disadvantage of the unusually long periods at time that were necessary in the prior oxidation processes, they have not entirely eliminated all the commercial disadvantages in that they do require special equipment for carrying out the processes. V

In accordance with the present invention I have found that the coking characteristics of swelling and caking bituminous coals can be altered by treatment with various inorganic 'ganic acids to react with ash-producing Among the various reagents that have been acids, mixtures of inorganic acids, or mixtures of inorganic acids and oxidizing salts. My proc- .ess is applicable to the treatment of coking bituminous coals generally and it may be used for treating the highly swelling and caking coals such as the Pittsburgh seam coals as well as the less highly swelling coals of the Beckley seam type. when the Pittsburgh seam coals are treated by this process the coking characteristics are altered to such an extent that theyv can be briquetted and subjected to carbonization operations in which the temperature rise through the plastic temperature range can be carried out at,

r the rate of at least 2 C. per minute using coal tar or pitch as a binder. Goals of the Beckley seam type can be treated by this process to alter the coking characteristics to such an extent that they can be compressed into briquettes using coal tar or pitch as the binder and then subjected to carbonization treatments in which the temperature rise permitted in the plastic temperature range is in the order of 2 to 2 /2-C. per minute. It is readily seen, therefore, that any bituminous coal capable of coking can be altered by my coals to be briquetted and carbonized under practical conditions and which also makes possible the use of a wider choice of bidders.

Briefly, my invention comprises treating finely ground bituminous coals with various inorganic acids, mixtures of inorganic acids or mixtures of inorganic acids with oxidizing salts at temperatures of from 90-250 C. for about 5 to minutes. The temperature at which the treatment :is carried out and the rate of temperature rise will of course vary with the particular coal being treated, the acid used, strength of acid, and also the binder which is to be used in the subsequent briquetting operations. In any event, the process can be so regulated that it is possible to prede- 4 'termine the exact conditions under which the process should be carried out to effect the necessary suppression of swelling and caking tendencies of the coals.

the processing rate of the coal can be increased. For example, an untreated coal which swells badly at a processing rate of 1 C. temperature rise through the plastic stage, can, after the acid treatment be processed at a rate of 2 C. per minute. The process is easily controlled and the coking characteristics of coals such as those of the Pittsburgh seam type can be altered in varying degrees. For example, the treatment canbeused to change the characteristics of such coals to 5 ment should be somewhat more severe in order to 6 compensate for the swelling and slumping which accompanies the use of such a binder.

' The present invention should not be confused with prior processes of treating coals with inorconstituents or for the purpose of removing sulfur and phosphorous compounds from coals. These prior acid treating processes were for the purpose of removing certain objectionable constituents from the coal, whereas the present acid treating process is for the purpose of increasing the rate of processing bituminous coals in carbonization processes without undue swelling or slumpprocess in a manner which will permit the 25 The acid treatmentof the various f coking bituminous coals can be so regulated that 5 found to be useful in carrying out my process are the inorganic acids such as sulfuric, nitric, hydrocomparatively cheap. The following specific tests,

carried out on different coking coals will serve to illustrate the operativeness of the present invention and also the flexibility of the invention when applied to different coking coals.

A sample of Ocean coal of the Pittsburgh seam was ground to -28 meshand then mixed with 1.6% of a 1.85 specific gravity sulfuric acid (which had been diluted with one-half its weight of water). The mixture was then stirred and heated to a temperature of about 150 C. for five minutes.

The mixture was then iiuxed with 8% of an acidtreated tar binder and compressed into briquettes. These briquettes were carbonized at a temperature rise oi. 2 A C. per minute through the plastic temperature range. At the same time there was carbonized along with these briquettes, briquettes made from the same coal ground-to the same mesh but which had not been treated by fiuxing with the sulfuric acid at 150 C. The briquettes made from the acid treated coal were unswollen while the ones which had not been treated were badly swollen.

In another test a sample of -28 mesh Beckley seam coal was fluxed with 1.6% of a 1.8 specific gravity sulfuric acid (diluted with one-half. its

weight of water). This mixture was slowly agiti ted and heated to a temperature of about 130 C. for about5 minutes after which the burners were turned off and the mixture agitated until the temperature had dropped to about C. Then 8% of 9. treated tar binder was added and fluxed thoroughly with the coal which was then transferred to a plant roll press and briquetted. The briquettes were carbonized at a rate of 2 C. per minute through the plastic temperature range. About 25% of the briquettes were appreciably swollen while the remaining 75% were only very slightly swollen and there was no sticking together of the briquettes. This Beckley seam coal cannot normally be fiuxed with a tar binder, briquetted and carbonized at a temperature rise of more than 1 C. per minute. Further tests carried out on the same coal indicated that when higher temperatures of from 200-250 C. were used, a smaller amount of acid was required to produce equivalent results.

Further tests were carried out on a sample of drochloric acid, perchloric acid, mixtures of suliuric and nitric acids, and mixture of sulfuric and hydrochloric acids were used. These tests a were carried out on a laboratory scale in which a 50 gram sample of the -28 mesh coal was mixed with the acid inorganic oxidizing reagent in a suitable container and then heated to the desired temperature after which the coal was fiuxed with 8% of a sulfuric acid treated tar, briquetted on a hydraulic press, and carbonized in a laboratory retort at 2 /e C. per minute rise through the plastic range with a superimposed steel bar head load. The results are tabulated in the followin table.

Similar laboratory tests were also conducted on a Beckley seam coal, the results of which are tabulated in the following table.

Table 1 Temperature Descri ti i la d No. Acid used treatment Bin n aa ggbcn e 1 None None... None v6 badl swell 2 ..do 160 also. treated m. No gwellin g a A 1 o s on coal 150 0 3: on coal v all 1m 11 qua reg cry 5; swo en. 4 Aqua rezia. 1.6 100 Nggioegblo improvement on o. 6 1.8 sp. g. HaSOl diluted with 50% B20- 150 c --d0 No swelling,

1.6% of 1.8 s 3. acid on coal. 6 1.4 sp. g. HN 1.6 0 on coal 150 0-- do. Somewhat swollen. 7 50/50 11.50. and RN 1. 1.6% on coal" 150 0 --do Blight swelling, 8 70% HCIOrH 11:0. 1.6% on (waL-.. 150 0-- do N swelling 9 70% H010 1.6% on coal Ngne, cold None Do,

10 70% E0104. 1.0% on coal None, cold H1804 treated tar. Not as good as No. 8 showing 8% taron coal. melded benefit 0! 150 heat- 11 70% 11010.. 0.8% on coal N313 cold dn Not quite as good a No. l0. l2 70% H0104. 1.6% 011 00a 00 0 d0 Not quite a good as 8,

a period of at least five minutes to reduce the swelling and caking properties thereof and then compressing into briquettes and subjecting said Table 2 Temperature Decal tion 0! carbonlze No. Acid used treatment Binder v mm d 1. None --s None H2504 treated tar. Appreciably swoilen,

' 8% tar on coal.

2 707 H0104. 0.8% on coal ---do --d0 Home improvement on No. 1. a 70 11010;. 0.8 on coal 00 0 d0 Some im rovement on No. 2. 4 70% H0104. 1.6 ,on coal 1 0 C No swelling In the foregoing example acid-treated coal tar was used as the binder in the production of briquettes. This binder comprises a 10% mixture of 60 B. sulfuric acid and coal tar. The present invention, however, is not limited to the use of such a binder. In briquetting operations the difliculties' due to swelling and caking are usually more apparent with a pitch or tar binder than with certain other binders. It is thereforev an advantage of the present invention that my pretreating process does permit the use of coal tar or pitch as a binder. On the other hand, when it is desirable to increase the head load bearing strength of briquettes, sulfite liquor may be used as the binder. In any event, the present invention can be used to alter the coking properties of any bituminous coal which will permit the coal to be coked at a faster rate of temperature rise through the plastic temperature range without swelling than would be possible if the coal had not been so treated. It is also an advantage of this invention that the processcan be so regulated that in briquetting operations any of the ordinary binders may be successfully used.

WhatI claim is:

1. A method oi. making carbonized briquettes from coking coals. which comprises treating badly swelling and caking coals-with from about 1 to 2% of an acid inorganic oxidizingreagent at a temperature within the range of 90 to 250 C. for a period of at least five/minutes to reduce the swelling and caking properties thereof and then compressing into briquettes and subjecting the briquettes to carbonization at a temperature rise of at least 2 C. per minute through the plastic temperature range.

2. A method of making carbonized briquettes from Pittsburgh seam coals which comprises treating saidcoals with from about 1 to 2% of an acid inorganic oxidizing reagent at a tem-- perature within the range of 90 to 250 C. for

briquettes to carbonization at a temperature rise of at least 2 C. per minute through the plastic temperature range.

3. A method of making carbonized briquettes from Beckley seam coals which comprises treating said coals with from about 1 to 2% of an acid inorganic oxidizing reagent at a temperature within the range of to 250C. for a period of at least flve minutes to reduce the swelling and caking properties thereof and then compressing into briquettes and subjecting said briquettes to carbonization at a temperature rise of at least 2 0. per minute through the plastic temperature range.

4. A method of making carbonized briquettes from coking coals which coals cannot normally be compressed into briquettes and carbonized at a temperature rise of more than /z C. per minute through the plastic stage without badly swelling and caking which comprises pulverizing said coal and subjecting the pulverizing coal to a treatment with from about 1 to 2% of an inorganic oxidizing acid at atemperature within the range of 90 to 250 C. for a period of at least five minutes to reduce the swelling and caking properties thereof so that when compressed into briquettes and subjected to carbonization the carbonization can be carried out at a temperature rise of at least 2- C. per minute through the plastic temperature range.

5. A method of making carbonized briquettes from Pittsburgh seam coals which coals cannot normally be compressed into briquettes and carbonized at a temperature rise of more than A2 C. per minute through the plastic stage without badly swelling and caking which comprises pulverizing said coal and subjecting the pulverized coal to a. treatment with from about 1 to 2% of an inorganic oxidizing acid at a temperature within the range of 90 to 250 C. for a period of at least five minutes to reduce the swelling and cakine properties thereoipso that when compresseddinto briquettes and subjected to carbonization the carbonization can be carried out 3 at a temperature rise of at least 2 C per minute through the plastic temperature range.

6,.A method of making carbonized briquettes from Beckley seam coals which coals cannot norwithin the range of so to 2505c. m a period of 1' at least flve minutes to reduce the swelling and caking properties thereof so that when com pressed into briquettes and subjected to .car-

bonization. the carbonization can be carried out at a temperature rise of at least 2 C. per minute through the plastic temperature range.

7. A process according to claim 4 in which the inorganic acid is sulfuric acid.

10 8. A process according to claim 3 in which the inorganic acid is perchloric acid.

9. A process according to claim 4 in which the inorganic acid is aqua regia.

. CLAYTON S. WOLF. 

